1. Field of the Invention
The present invention relates to an improved method for forming wide area features on green ceramic dielectric layers for forming multi-layer ceramic substrates for electronic applications, and for metallizing said wide area features with electroconductive paste composition without contaminating adjacent surface areas of the dielectric green layers.
2. Discussion of State of the Art
It is known to form vias and circuit outlines on greensheets or layers of dielectric composition, and to fill said vias or circuit outlines with electroconductive paste composition to produce X- and Y- interconnections with electrical circuits printed on said dielectric sheets or on contacting surfaces of adjacent dielectric sheets, and to produce transverse conductive pads and vias providing conductive interconnections with portions of conductive circuits printed on other dielectric sheets of the multi-layer ceramic substrate which are otherwise insulated therefrom and/or insulated from the electrical leads of the MLC substrate.
A preferred method for forming complex and high precision vias and recessed channels and/or fine, closely-spaced lines in green ceramic layers, and for filling said vias and channels with the electroconductive paste without the need for precision printing systems or preformed masks and alignment systems is disclosed in commonly-assigned U.S. Pat. Nos. 3,948,706, 3,956,052 and 5,145,551. The methods of these patents comprise heat-and-pressure laminating a thin, inert metallized film of a thermoplastic organic polymer to the surface of the dielectric greensheet, thermally machining the vias and/or circuit outlines through the film and into and/or through the greensheet, using electron beam or laser radiation to ablate and remove the film and the greensheet composition from the affected areas. Next an electroconductive paste is wiped over the film and deposited in the via areas and/or circuit areas to fill said areas while the other surface areas of the dielectric greensheet are masked by the film against contact therewith. Finally, the surface film is peeled away, and the electroded greensheet is assembled with other similar conducting and insulating layers to form a MLC which is fired to form a unitary component.
The prior known methods are extremely useful for the formation of narrow vias and fine-line recesses but are inefficient for the total removal of larger masses of masking film for the metallizing of large features such as seal bands, wire bond pads and I/O pin pads.